1. Technical Field
Example embodiments relate to a semiconductor memory device having a recessed control gate electrode.
2. Description of the Related Art
Semiconductor memory devices have become more integrated and faster in operation in response to the recent trend toward smaller and faster devices in the semiconductor industry. For example, three-dimensional (3-D) semiconductor memory devices have been introduced as alternatives to conventional planar semiconductor memory devices. A 3-D semiconductor memory device may include a control gate electrode recessed in a semiconductor substrate.
3-D nonvolatile semiconductor memory devices may have higher channel areas and operating currents than conventional planar semiconductor memory devices. The higher operating currents may result in increases in the speeds of the 3-D semiconductor memory devices. However, unit cells of the 3-D semiconductor memory devices may occupy relatively large areas and operate at a one bit level, thus presenting obstacles to increasing the integration density of the 3-D semiconductor memory devices.
Additionally, source and drain regions of the 3-D semiconductor memory devices may also occupy relatively large areas. For example, negative AND (NAND) type semiconductor memory devices may be configured such that the source and drain regions are alternately arranged, thus occupying relatively large areas and limiting integration density. Furthermore, the distribution of the electric field density of the 3-D semiconductor memory devices may not be uniform, thus decreasing efficiency and reliability in the programming and erasing operations.